Ionization of gaseous molecules is conventionally initiated by photon bombardment, charged particle impact, ultraviolet radioactive ionization, or by thermal electron beams. Such ionization techniques are typically utilized for mass spectrometers and ion mobility spectrometers. During ionization, depending on the level of impact energy, one of two events occur, either electrons are ejected from atoms and molecules or the molecules themselves are fractured into complement of fragments with diverse charge states. These processes are known as hard ionization and while they can be utilized to provide a measurement indicative of the atoms and molecules contained within the ionized sample, many components cannot be measured. Further, these ‘hard’ ionization mechanisms are inefficient with approximately 0.1% of atoms or molecules ionized. In addition, conventional mass spectrometers require low pressure (“hard vacuum”) to operate to prevent higher velocity ions from colliding with a slower moving atoms and molecules (thermal velocities) that, during passage through the spectrometer, attenuate ion currents below detectable limits.
Moreover, conventional systems for ionization are susceptible to avalanche arcing when gases ionize in high electric fields. This phenomenon results because the mean free path length between molecules (at the relevant gas pressure) is greater than the electrode separation within the ionization device (empirical measurements showing the breakdown voltage versus gas pressure are identified in the Paschen curve of FIG. 1). If conventional systems could be configured to operate under the Paschen curve, then ionization would occur without avalanche arcing.
Current ionization systems coupled to detection systems are unable to characterize a wide range of biological matter. This is due in part because most biological matter comprises complex molecular structures that are susceptible to fracture, thus making it hard to characterize. In addition, some biological matter such as bacteria have varying masses depending on the stage of replication. Accordingly, as conventional techniques necessarily fracture the biological matter, users are forced to examine a spectrum of mass data corresponding to the various atoms and molecules that made up the examined matter rather than the overall mass of the biological matter.
In addition, there are many applications that utilize an ion or electron source that would benefit from a low cost efficient replacement such as field emission cathodes coated with low effective work-function materials. However, such cathodes are difficult and costly to manufacture and often have wide range of emissions and so there remains a need for an improved electron source.
It will be appreciated that there are other applications that are desirable for ionization including the characterization of ions by their valiancy, if an ionization system were sufficiently “soft”, efficient, small and inexpensive, and it is to this end that other aspects of the invention are directed.